freeDiameter, a free/open source Diameter protocol implementation is now available for Fedora/RHEL. Install it using:

$ sudo yum install freeDiameter freeDiameter-devel

It fully supports the Diameter Base Protocol as specified in RFC 3588, Diameter Extensible Authentication Protocol (EAP) application server from RFC 4072, and Diameter Session Initiation Protocol (SIP) application from RFC 4740. Thanks to Sebastien Decugis for accepting the upstream patches.